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Genetics: Linkage, Recombination, and Quantitative Traits - Prof. James Birchler, Study notes of Genetics
This document delves into the concepts of linkage, recombination, and quantitative traits in genetics. It explains how genes residing on the same chromosome pair (linked genes) can be separated through recombination events, and how the frequency of recombination can be used to determine the order of genes on a chromosome. The document also explores the concept of quantitative traits, which are controlled by multiple genes and influenced by environmental factors. It discusses how the number of genes involved in a quantitative trait can be estimated by analyzing the distribution of phenotypes in a population.
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2023/2024
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Test 2 Review Slides
Recombination
Recombination- exchanges parts of homologous pairs AB X ab = A/a B/b One parent Second parent F 1 AB = parental type ab = parental type Ab } recombinants aB } recombinants
Linkage- genes residing on the same chromosome pair. Genes A/a B/b Both recessives on same member of a chromosome pair = coupling A B a b Dominant and recessive on opposite members of a pair. = repulsion A b a B
- Any one recombination occurs between 2 of 4 chromatids, one each from a homologue, but never between sister chromatids.
- Two of 4 chromatids are recombinant and 2 are parental.
6. In each meiosis, recombination occurs
at different places along the chromosome.
Hypothesis: Lack of Linkage
- (^) Are these values due to linkage OR to chance deviation from independent assortment? How many degrees of freedom do we have? If probability is > 0.05, accept “lack of linkage” = chance deviation from independent assortment
Our Chi 2 = 5.2, with 3 df Accept “lack of linkage” (chance deviation from independent assortment)
Mapping
Mapping
- (^) Linked genes can be mapped relative to
each other.
- (^) Provides information about how genes are
organized on the chromosome and for
isolation of a gene.
- (^) We can use recombination frequency to
determine the order of genes.
The ABC’s of Mapping If the order is: If the order is: If the order is: The gene that switches in the doubles class is the one in the middle.
Coefficient of coincidence- the fraction of expected double crossovers that actually occur. Interference- the fraction of expected double crossovers that are inhibited from occurring.
Practice problem a+ (^) b+ c+ b c^ c c b b a a a a is 15m.u. from b. b is 20m.u. from c. How often will you get a+ b c+ offspring?
Practice problem a+ (^) b+ c+ b c^ c c b b a a a a is 15m.u. from b. b is 20m.u. from c. How often will you get a+ b c+ offspring?